This invention relates to a refrigeration system expansion valve, and more particularly to a thermostatic expansion valve having means enabling a service person to conveniently adjust (i.e., calibrate) the superheat setting of the expansion valve from a location remote from the valve.
In a typical refrigeration system, high pressure liquid refrigerant is expanded in an expansion valve incorporated in the liquid refrigerant line between the condenser and the evaporator coils. The low pressure, low temperature refrigerant discharged from the expansion valve is then directed through the evaporator coil for absorbing heat and thus refrigerating the space surrounding the evaporator coil. The expansion valve is adjusted to control the refrigerant flowing into the evaporator coil to a rate sufficient to maintain a desired temperature of the evaporator coil. More specifically, a thermostatic expansion valve meters the flow of refrigerant into the evaporator in proportion to the rate of evaporation of the refrigerant in the evaporator, and is responsive to the temperature of the refrigerant leaving the evaporator and to the pressure in the evaporator. In this manner, a thermostatic expansion valve can control the refrigerant leaving the evaporator at a predetermined superheat. Generally, the superheat of the refrigerant is a measure of the heat contained in the refrigerant vapor above its heat content at the boiling point (saturation temperature) at the existing pressure (i.e., the heat content of the refrigerant vapor exiting the evaporator coil which is in excess of the heat content of the vapor which normally could be expected at the refrigerant pressure as it exits the evaporator). By ensuring that the condition of the refrigerant entering the suction line from the evaporator is at a desired superheat level, the performance of the refrigeration system can be enhanced and also the return of liquid to the compressor is prevented.
A thermostatic expansion valve typically includes a spring-biased metering valve which regulates the flow of liquid refrigerant through the expansion port to the evaporator. A thermostatic bulb charged with a volatile substance is positioned in heat exchange relation with the suction line of the refrigeration system at the outlet of the evaporator. The thermostatic bulb is interconnected by means of a capillary tube to a diaphragm actuator included on the thermostatic expansion valve with the diaphragm actuator being mechanically interconnected to the metering valve of the thermostatic expansion valve. A rise in the evaporator temperature will increase the temperature of the evaporated gas passing through the suction line (i.e., increase its superheat) which in turn is sensed by the thermostatic bulb. The thermostatic bulb absorbs heat and the volatile substance therein increases its pressure and thus causes the diaphragm actuator to open the metering valve of the expansion valve and to thus proportionately increase the flow of refrigerant. Upon cooling of the evaporator, the temperature of the refrigerant discharged from the evaporator will decrease which in turn is sensed by the thermostatic bulb thereby resulting in the metering valve of the thermostatic expansion valve to at least partially close and to block at least a portion of the refrigerant flowing to the evaporator.
A thermostatic expansion valve is typically provided with an adjustment screw for varying the operating point (i.e., the superheat setting) of the valve at which the metering valve blocks or unblocks the expansion valve when the thermostatic bulb is at a specified temperature. As is conventional, this adjustment screw varies the compression of a spring biasing the metering valve member toward its closed position. Even when the thermostatic expansion valve is sized properly in relation to its respective refrigeration system, the adjustment of the thermostatic expansion valve is critical to the satisfactory and efficient operation of the refrigeration system.
In refrigeration systems, such as in refrigerated display or freezer cases installed in supermarkets, or in large ice making machines, the thermostatic expansion valve is typically located within the display case cabinet proximate the evaporator coils. While the thermostatic expansion valve may be set or calibrated prior to or during installation of the refrigerated display case, it is oftentimes not known whether the valve will be properly set once the display case is filled with meat, frozen food, or the like. In many refrigerated display cases, the expansion valve is accessible only by unloading the product from the display case and by removing service panels in the display case cabinet. Then, the superheat setting of the expansion valve may be adjusted, the service panels replaced, and the product again loaded in the refrigerated space. The unit must then be allowed to stabilize in order to check the setting of the expansion valve. Oftentimes, to properly adjust the expansion valve, several adjustments must be made until the optimum operating conditions of the refrigeration system are attained. Because this procedure requires a good deal of time and effort on the part of the serviceman, this is oftentimes not done and many refrigerated display cases are permitted to operate for extended periods of time at inefficient operating conditions thus wasting considerable amounts of energy.
Among the many objects and features of the present invention may be noted the provision of a thermostatic expansion valve, such as described above, located within a refrigerated appliance (e.g., a refrigerated display case or the like) proximate the evaporator coils thereof and being conveniently adjustable from the exterior of the refrigerated appliance at a location remote from the expansion valve;
The provision of such a thermostatic expansion valve which allows accurate calibration of superheat setting of the expansion valve to match the load conditions of the refrigeration system while the refrigerated appliance is in operation without the necessity of unloading the refrigerated appliance or without the necessity of removing service panels from the appliance for access to the expansion valve;
The provision of such a thermostatic expansion valve which can be accurately calibrated to a desired superheat setting thereby to enhance the operating efficiency of the refrigeration system; and
The provision of such a thermostatic expansion valve which is economical to manufacture, easy to install in a refrigerated appliance, and which is reliable in operation.
Other objects of this invention will be in part pointed out and in part apparent hereinafter.